The present invention relates to pulse-absorbing bags for automobile gasoline filters and methods for making the same. Such bags and similar devices for preventing water hammer have been commonly used in the plumbing industry for years but, only recently, has a need for them been recognized in the automobile industry.
Collapsible plastic bags may be incorporated within the gasoline filter housings, or other appropriate in-line locations, of certain types of automobiles to absorb the pressure increase and shock created by sudden injections of gasoline which is non-compressible and cannot absorb such pressure fluctuations. In such a manner, the bags prevent the collapse of the filters themselves, and suppress the annoying "hammer" pulsations which would otherwise result. The "hammer" effect is especially noticeable with larger vehicles using big fuel pumps, and in particular those vehicles embodying a fuel injection system wherein the in-line pressure is generally cyclical.
To provide and maintain sufficient resiliency, the bags must be filled with a gas, and must be impermeable to both such gas and the fuel itself. Therefore, nylon is a preferred material because of its low permeability by gases, its flexibility, and its strength. However, since nylon is oxidizable and slightly permeable by air, air is an undesirous gas for enclosure within the bags and must be avoided. Thus, methods are needed to produce bags enclosing the preferred gas and eliminating air.
One prior art method for making such an article comprises nozzle injecting a positive pressure of the preferred gas between two parallel sheets of plastic; peripherally sealing the two sheets together and over the end of the nozzle by opposing primary dies, each die having a central concave surface for forming a pillow-shaped bag and opposing grooves on one side for positioning the nozzle; removing the nozzle after pressurizing the bag; and sealing the bag opening, which remains at the nozzle positioning grooves, by secondary dies immediately adjacent the primary dies. Such a method is obviously complicated and requires accurate timing between removing the nozzle and finally sealing.